This invention relates generally to treatment of granular activated charcoal (GAC) filtration systems; and more particularly it concerns use of micro-organisms for removal of contaminating hydrocarbons from such systems.
“Liquid phase” GAC systems are typically used as water filtration media to adsorb toxic chemicals found in wastewater and extracted groundwater plumes. Treated water typically must meet Clean Water Act standards for discharge into sewers or streams. GAC becomes spent when its adsorption potentials are met and breakthrough of toxics occurs. There is need for apparatus and methods that not only extend service life, but also, actively effect scrubbing of the effluent water stream to mitigate GAC breakthrough of daughter degradation compounds such as Tri-Butyl Alcohol (TBA), which is created in the breakdown of Methyl Tertiary Butyl Ether (MTBE), the clean fuels additive found in gasoline.
More generally, granular activated carbon or charcoal (GAC) is used extensively to treat water, wastewater and groundwater at remediation sites contaminated with various organic pollutants such as petroleum hydrocarbons including BTEX and MTBE, chlorinated solvents, volatile and semi-volatile organic compounds. Historically, this technology has been used because it is effective, predictable, economical, and simple to implement at a variety of sites and operating conditions. Recently, however, increasing regeneration costs and the regulation of compounds that have lower adsorption efficiencies has made traditional GAC systems less economical. For example, hundreds of sites across the United States and overseas with groundwater impacted by MTBE, and its daughter products including TBA, must be remediated to near non-detect levels, but GAC has a very low adsorption efficiency for MTBE and TBA. The result is that MTBE and TBA breakthrough occurs very rapidly and carbon change-out frequencies must increase.
Such toxic chemicals include for example tri-butyl alcohol created in the breakdown of MTBE, Methyl Tertiary Butyl Ether, the clean fuels additive found in gasoline.
As noted, granular activated carbon (GAC) is used extensively to treat groundwater and vapor streams at remediation sites and industrial facilities across the U.S. and abroad. To date, the standard practice has been to replace spent carbon with virgin carbon, or to have the carbon thermally regenerated. Replacing spent carbon with virgin carbon is more expensive, but is often done since the alternative thermal regeneration breaks down the carbon, resulting in more “fines”. The cost of thermal regeneration has also been increasing due to increasing energy costs. At the same time, the increasing presence of MTBE and its daughter products like TBA have resulted in increasing carbon usage rates and expense, since GAC has a lower adsorption efficiency for these compounds.